This is an application for a K24 Midcareer Investigator Award in aging-related patient-oriented research. The candidate is a professor of psychiatry and epidemiology at the University of Pittsburgh with an established track record as a researcher, clinician, and educator. The proposed research is focused on Mild Cognitive Impairment (MCI), a variably defined condition generally regarded as a prodromal and/or risk state for AIzheimer's and other dementias. Its basic premise is that current "diagnostic" criteria for MCI do not reflect the real-world distribution and outcomes in older adults in the typical community or clinical setting. In particular, MCI may be unstable and heterogeneous especially in patients with significant comorbidity and on multiple medications. The aims of the Research Plan are to refine the criteria and propose new ones developed from: (1) analysis of existing data on MCI from a completed 15-year longitudinal community-based study of an aging cohort, and (2) an added focus on MCI in an ongoing study of older primary care patients. The refined criteria will be applied to (3) a new multicenter cohort study, for which methods and criteria will be derived from the preceding two components and pilot data will be collected during the K24. The Mentoring Plan is targeted towards beginning clinician investigators with excellent clinical and academic backgrounds and a commitment to clinical research in dementia and mild cognitive impairment. Trainees will obtain hands-on experience of patient-oriented research by conducting research assessments of patients participating in the ongoing primary care study (part 2 above), under supervision by the K24 awardee, and participating in the multidisciplinary consensus diagnosis conferences. They will also obtain supervised experience of analyzing, interpreting, and reporting data from the completed community study (part 1 above) for publication. A range of additional didactic and experiential programs is available depending on their interests and previous background. Each trainee will develop an independent research project application as part of the training and be evaluated on acquired knowledge, skills, and productivity.